tion to working mines should be made a part of every school's curriculum. At least two of our universities have of late adopted a summer school plan, in which classes spend several weeks in the field, making detailed studies of this nature.

Geology is not reckoned as an exact science. Yet the mining geologist is expected to make it sufficiently exact to warrant the investment of thousands of dollars. He, of all geologists, needs the most comprehensive training.

GEORGE P. MERRILL.

STRUCTURAL RELATIONS OF THE WISCONSIN ZINC AND LEAD DEPOSITS.

Sir: The interesting and instructive paper by Professor Grant in the preceding issue of this magazine on the above subject accords with one of the structural relations in which zinc ores occur in northern Arkansas. Dr. J. C. Branner, ex-state geologist of Arkansas, has already called attention to what he considered a tendency of the ores of the region to collect in synclines,1 but it was not his intention for the statement to be taken for any more than a suggestion to future workers in the field. Taking advantage of this suggestion as a guide to observation, the present writer, after a good deal of field experience in the region named, has become convinced that the synclines are favorable places for ore accumulation.

The rocks in which the zinc usually occurs, like those in the Wisconsin region, are of Ordovician age, and consist of magnesian limestone containing a good deal of chert in nodules, and a few thin beds of sandstone. They also contain a small amount of shale, but in no place observed by the writer is ore associated with or near it. For the most part they are horizontal.

When out of the reach of atmospheric agencies, the ore is the sulphide, whether above or below the groundwater level, except in the cases in which it is closely associated with sandstone, when it is a silicate (calamine). The sulphides of iron and lead but rarely occur associated with the zinc. Dolomite is the most com'Geol. Surv. of Ark., Vol. V., 1892, p. 32.

monly associated mineral. Most of the profitable ore occurs in joints, which were formed presumably at the time of folding, though some of it is disseminated. The disseminated ore is quite generally distributed through the Ordovician rocks of the region at certain horizons, but only in synclines or other structural features has it collected in such quantities as to attract the prospector. Everything points to these rocks being the source of the ore, which has been leached out by the circulating underground water and concentrated along favorable places for movement, of which the syncline is one.

Other favorable places for ore accumulation in the Arkansas field are faults, and the crests of small anticlines in which the most brittle beds are much broken, apparently from rather rapid folding of the rocks. In the latter case, the broken beds are cemented into coarse breccias by dolomite which in places carries more or less sulphide of zinc.

A. H. PURDUE

REVIEWS

The Nature of Ore Deposits.

By DR. RICHARD BECK, Professor of Geology and Economic Geology in the Freiberg Mining Academy. Translated and revised by WALTER Harvey Weed, E.M., geologist, United States Geological Survey, with two hundred and seventy-two figures and a map. First edition in two volumes, New York and London Engineering and Mining Journal, 1905.

The first edition of Dr. Beck's "Lehre von den Erzlagerstätten" was was published in Berlin in 1901, and was followed by a second edition two years later, in 1903. Simultaneously with this second edition a French translation of the work appeared. The English translation by Mr. Weed, which has just been issued, may be considered as the third edition of the work.

Mr. Weed states in the preface that he was originally asked by the publishers to practically re-write the book from an American standpoint, giving greater prominence to American ore deposits, but that this idea was abandoned because it would involve serious abridgments of the descriptions of important foreign localities, which descriptions make the work especially valuable to American engineers and geologists. Mr. Weed has not, however, confined himself solely to translating the work, but has written new descriptions of many American ore deposits which have, of recent years, been carefully studied. The nomenclature employed in the German edition has in some few details been made to conform more closely to American usage, but otherwise the book is essentially identical with the last or second German edition with the exception of Mr. Weed's additions. In this English edition, however, the book appears in a form which is more conveniently handled; the single large volume of the German edition having been divided into two volumes. This division

has, however, been made, strangely enough, in the middle of a section without reference to the sense of the text, while by adding a few more pages to the first volume a much more suitable division of the subject matter could have been obtained. The book is clearly and simply written, and is well illustrated by cuts and diagrams. It is the most comprehensive general treatise on the subject of ore deposits which we now have in the English language.

After a preliminary section dealing with definitions and literature, the Classification of Ore Deposits is taken up.

The classification adopted is as follows:

(I.) Primary Ore Deposits.

A. Syngenetic; formed simultaneously with the country rock.

1. Magmatic segregations.

2. Sedimentary ores.

B. Epigenetic; formed later than the country rock.

I. Veins.

2. Epigenetic deposits other than veins.

(a) Epigenetic deposits; formed essentially by an impregnation of non-calcareous rocks, the deposits being generally in distinct beds.

(b) Epigenetic stocks; formed essentially by a metasomatic replacement of calcareous rock mostly in the form of stocks, pockets or stringers.

(c) Contact metamorphic ore deposits; ore beds and stocks formed through contact metamorphism caused by Plutonic intrusive masses.

(d) Ore bearing cavity fillings; deposits formed essentially by a simple filling of pre-existing cavities mostly in the form of stocks or stringers.

(II.) Secondary Deposits.

1. Residual deposits.

2. Placer deposits.

Each of the classes of ore deposits is then considered in succession, and some of the most notable examples described.

Under the head of Magmatic Segregations three classes are distinguished, namely:

1. Segregations of native metals.

2. Segregations of oxide ores.

3. Segregations of sulphide and arsenical ores.

With regard to group three it is stated "that the evidence that deposits of this class are direct segregations from a molten magma is not as clear and conclusive as it is in the case of groups one and two." This, it is affirmed, is particularly true of the Norwegian nickeliferous pyrrhotites and it is added that recent microscopic study has proved that the Sudbury deposits are metasomatic replacements and that there is "not a single example of magmatic copper deposits known in North America.” Whether this conclusion is justified or not the readers of EcoNOMIC GEOLOGY will, it is hoped, have an opportunity of judging for themselves after reading a series of papers on these Sudbury deposits, which will appear shortly in this magazine, by several gentlemen who have devoted special study to these deposits and who are in a position to speak authoritatively concerning them.

The Bedded Ore Deposits, which are next considered, are represented by a large number of occurrences, chiefly European, which are well described. Among the American deposits of this class are the ores of the iron ranges of Lake Superior. The treatment of these is rather inadequate, and it would seem better, even at the cost of slightly enlarging the book, to have presented a more complete and better balanced account of what are in fact the most important iron deposits in the world. In the account as given there are some inaccuracies. Thus, on page 78 the

"soft ores

are said to be brown hematite. These ores, how

ever, do not hold sufficient water to be so classed, for while undoubtedly specimens of brown hematite can be obtained from these soft ores, they, as a class, are essentially red hematite, only partially hydrated, the average content of water in the Marbeing about 5.4 per cent., while in the Mesabi Range,

quette ores

whose product may be said to consist entirely of soft ores, the average content of water is only 7 per cent., while brown hematite has twice this amount of water. Again, on page 23, the